There is a massive amount of material in the port roof of these heads from about midway down the runner to the manifold face. The port's roof shape is cast concave (which is good), and our porting exaggerated this form even further. Raising the roof entrance provides a much better approach into the runner, but precludes the use of the stock gaskets or valley pan. We cut the roof .300 inches at the entrance. We'll have to get creative to make a manifold work with this.